Exemplary embodiments of the present invention relate to a heat exchanger for the refrigerant circuitry of a vehicle air-conditioning system. Such a heat exchanger is configured to include a header pipe and allow a pass flow in a multi-pass way and bidirectionally. The air-conditioning system is configured to perform a combination of cooling mode and heating mode. The flow direction of a refrigerant within the heat exchanger depends on operation mode.
Furthermore, the present invention relates to an apparatus for partitioning the internal volume space of the header pipe of a heat exchanger and changing the flow of a fluid in the header pipe of the heat exchanger.
A conventional air-conditioning system for a vehicle is formed of a combined cooling device and heat pump system. A heat exchanger configured to operate as a condenser in cooling device mode and to discharge heat from a refrigerant to ambient air functions to absorb heat from ambient air as an evaporator in heat pump mode.
According to a prior art, for example, a supercooling section and an integrated high-pressure accumulator are formed in a heat exchanger, that is, a multi-pass heat exchanger used as the condenser. In the refrigerant circuitry of a vehicle air-conditioning system, the condenser basically includes 2 or 4 passes. A face in which heat exchange is performed is formed of flat tube profiles connected by ribs on the air side. When fabricating such a heat exchanger, the flat tube profiles are inserted into header pipes in which slots are formed on both ends thereof on the refrigerant side and then soldered. In order to change the direction of the refrigerant mass flux, a separation component is provided. The slots are provided on a wall at desired locations on the outside of the header pipe using laser cutting or stamping, for example, and the flow cross sections of the header pipes are closed by a small-sized and stamped plate. In this case, the small-sized plate corresponds to the separation component. By using the separation component, the heat exchanger is partitioned into, for example, 2 or 4 partial regions, so-called passes. By using the separation component, the heat exchanger is partitioned from the refrigerant side to n+1 passes.
In particular, when the air-conditioning system operates in cooling device mode, in a heat exchanger used as the condenser, a high-pressure accumulator is conventionally disposed between the second last pass and the last pass in the case of a system including thermostatic expansion valves. Such an accumulator is disposed and formed in the condenser. In the accumulator, the phases of an almost condensed refrigerant are separated from each other. Thereafter, a settled liquid refrigerant flows through the last pass of the condenser. Accordingly, a liquid refrigerant that has a much higher density than a gaseous refrigerant and that requires a flow cross section smaller than a two-phase mixture may be applied to the last pass. For such a reason, in the prior art, the last pass has a supercooling section that has much smaller flat tubes than those of previous passes.
In addition, the condenser may include a filter screen and dry means.
When the refrigerant circuitry operates in heat pump mode, the same heat exchanger is used as the evaporator. In this case, the refrigerant expands to a pressure level at which a corresponding saturation temperature is lower than temperature of ambient air. Accordingly, the refrigerant absorbs heat from the ambient air and discharges the absorbed heat.
An expanded 2-phase refrigerant is flown and evaporated through the original supercooling section. The section of the heat exchanger that operates as the evaporator is a section designed to allow the pass flow of a liquid refrigerant, a much higher density according to a small number of flat tubes, and a small flow cross section based on the much higher density. The section of the heat exchanger has a very high pressure loss in heat pump mode. This is because the density of the refrigerant is reduced according to an increase of evaporation.
The density of the refrigerant in heat pump mode becomes very low on the lower pressure side of the refrigerant circuitry due to the low pressure level. Accordingly, an additional flow pressure loss has a bad influence on performance and efficiency of a heat pump system.
Furthermore, in heat pump mode according to ambient air as refrigerant circuitry and a heat source in a temperature less than 0° C., there is a danger that the heat exchange surfaces of the heat exchanger operating as the evaporator may be frozen.
The multi-pass structure of a heat exchanger that generates a high pressure level on the refrigerant side due to a low absorption density of the refrigerant causes an additional drop of a surface temperature of the heat exchanger and an increase in the danger of freezing resulting from the additional drop.
There is known the assembly of components of refrigerant circuitry in which a heat exchanger formed to be supplied with external air operates in a flow direction that is alternated on the refrigerant side. In such an assembly, when the heat exchanger operates as the condenser in cooling device mode, the refrigerant flows through the heat exchanger in a first flow direction. In contrast, when the heat exchanger operates as the evaporator in heat pump mode, the heat exchanger is supplied with the refrigerant so that the refrigerant flows through the heat exchanger in a second flow direction opposite the first direction. In particular, when the heat exchanger operates as the evaporator in heat pump mode, a pressure level of the refrigerant is reduced. Accordingly, in heat pump mode, not a refrigerant that has almost been evaporated or overheated, but a refrigerant that is in a 2-phase state after decompression is flown through the supercooling section of the condenser in cooling device mode with a much higher density. However, a very high pressure loss that is disadvantageous in heat pump mode is merely reduced, but is not optimally reduced.
In a heat exchanger inserted into refrigerant circuitry that enables a pass flow bidirectionally for a heat exchange between the refrigerant and ambient air, how the freezing of heat exchange surfaces can be technically controlled and prevented when the heat exchanger operates in heat pump mode has been known in the prior art. In such a prior art, for example, a freezing process is avoided so that a heat pump is turned off in a surrounding temperature less than 0° C., or the refrigerant circuitry switches from heat pump mode to cooling device mode for at least short time in order to melt the heat exchanger and operates in cooling device mode. In the proposed methods, however, the air-conditioning system has a very low output reduction.
EP 1 895 255 B1 proposes a heat exchanger assembly in which two distribution pipes are spaced apart from each other in parallel, a plurality of flow tubes is extended between the two distribution pipes so that the refrigerant can flow between the distribution pipe, and the plurality of flow tubes forms a channel with the distribution pipe so that a fluid can pass therethrough. A static separator for partitioning the hollow space of the first distribution pipe into a first chamber and a second chamber having determined ratios is disposed in the first distribution pipe. Such a heat exchanger assembly includes connection parts disposed between the distribution pipes and an external control device configured to switch between evaporator mode and condenser mode. In this case, the connection parts are open and closed so that the refrigerant is circulated in the form of a single pass in evaporator mode and in the form of a multi-pass in condenser mode through all the flow tubes. In such a heat exchanger assembly, a pass flow as 2 passes, for example, is possible in evaporator mode. In such a case, the refrigerant flows through passes larger than 2 passes in condenser mode.